When a custom search index is created, a backend job is automatically triggered to process the initial data.
After this initial run, the system handles updates incrementally by indexing only new or modified records from the source, eliminating the need for manual intervention in most cases.
Manual rebuilds should be used cautiously, as they reprocess the entire dataset and can consume significantly more credits compared to incremental updates. The Process History feature provides visibility into indexing activity, such as the number of rows processed, but it does not differentiate between system-triggered and manually initiated runs.
Overall, the expected behavior is that the search index continuously and automatically reflects source data changes without requiring manual rebuilds.
References :
https://help.salesforce.com/s/articleView?id=data.c360_a_search_index_view_search_index.htm&type=5
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